The present invention relates to a printing method for forming a printing image directly on a printing medium, and in detail an ink jet printing method which, by adsorbing dust and foreign matter existing on a printing medium and removing the same therefrom, is able to bring about a sophisticated printing image by electrostatic type ink jet recording and is able to print at a high speed.
An electro-photographic system, a sublimation type and fusion type thermal transfer system, and an ink jet system, etc., are available as a printing method for forming a printing image on a printing medium on the basis of image data signals.
The electro-photographic system becomes an expensive apparatus whose system requires a process for forming an electrostatic latent image by electric charge and exposure on a photosensitive drum and becomes complicated.
The thermal transfer system is inexpensive as an apparatus, but since an ink ribbon is used, running cost thereof becomes high, and waste is produced.
On the other hand, the ink jet system is inexpensive as an apparatus, and since ink is discharged onto only an image portion required and direct printing is carried out on a printing medium, coloring agents can be efficiently used, and the running cost thereof is inexpensive.
A method for attaching an ink jet printing press to a web press and additionally printing varying numbers and marks, etc., on the same paper by the ink jet system is disclosed in, for example, Japanese Unexamined Patent Publication No. 10-286939, as a method for applying an ink jet technology to a printing system.
However, it is further preferable that high-quality image information such as a photo image can be printed. But, with an ink technology in which water-based or organic solvent-based ink containing prior art dyes or pigments as coloring agents is jetted under pressure, since liquid drops containing a great deal of solvent are discharged, there is a shortcoming in that blur occurs in a printed image unless expensive exclusive paper is used.
Therefore, where printing is carried out on normal paper or plastic sheets which are a non-absorptive medium, etc., no high-quality printed image can be obtained.
Also, as one of the ink jet technologies, there is a method for heating and fusing ink, which is solid at a normal temperature, and jetting fused ink to form an image. If this ink is used, blur of a printed image can be relieved. However, since the ink viscosity is still high when the ink is discharged, it is difficult to jet very fine liquid drops, wherein individual dot images obtained will have large areas and be thick, and accordingly, no fine image can be formed.
Further, in order to obtain high-quality images, it is necessary to keep the discharging state of an ink jet in good condition. However, dust and/or foreign matter adhered to a printing medium are adhered to a printing head and deposited there in line with use of the recording head, wherein if the recording head may stop or malfunction, there is a fear that the printed matter willing stained. That is, clear images are scarcely obtained.
The present invention also relates to a plate making method and plate making apparatus, which carry out making of a digital plate, and in particular a plate making method and a plate making apparatus, which bring about satisfactory plate quality and printing quality using oil-based ink.
The present invention relates to an in-press image plotting and offset printing method and an in-press image plotting and offset printing press in which digital plate making is carried out in a press. In further detail, the invention relates to a plate-making and printing method and a printing press that carries out printing upon performing plate making by oil-based ink and is able to bring about satisfactory plate making quality and satisfactory printing quality.
In offset printing, areas for receiving printing ink and those for repulsing printing ink are provided on the surface of a printing plate in compliance with an image document, and printing ink is adhered to the areas for receiving ink to carry out printing. Normally, hydrophilic and lipophilic (ink-receptivity) areas are formed on the surface of a plate as per images, the hydrophilic areas are made into an ink repulsing property, using dampening water.
With respect to recording (plating making) images on a printing master plate, generally, once an image document is analogically or digitally outputted on a silver salt photography film, a diazo resin and optically polymerizable photopolymer sensitive material (printing master plate) is exposed to light through the silver salt photography film, and non-imaging portions are eluted and removed mainly by an alkali-based solution.
Recently, in offset printing, in view of recent advancements in digital image plotting technologies and requests for an increase in processing efficiency, many systems for directly plotting digital image information have been proposed. This technology is called “CTP” (Computer-to-plate) or “DDPP” (Digital Direct Printing Plate). A system for recording images in an optical mode or a thermal mode by using, for example, a laser beam is available, and the system has been partially made into practical application.
However, the plate making system is such that in both the optical mode and thermal mode, treatment is made with an alkali developing solution after recording by a laser, and non-imaged portions are eluted and removed to make printing plates, wherein the alkali solution is discharged as a waste solution, and this is not favorable in view of the environment.
On the other hand, since, with a method using a laser beam, the apparatus becomes expensive and large-scaled, a system using an ink jet method by which an inexpensive and compact image plotting apparatus can be brought about has been attempted.
Japanese Unexamined Patent Application Publication No. 64-27953 discloses a method for making plates by plotting images by an ink jet using lipophilic wax ink on a hydrophilic plate material. With this method, a mechanical strength of image-plotted portions is weak because the images are formed of wax, and adhesivity with the hydrophilic surface of plates shortens, wherein print resistance thereof is low.
Further, it is necessary to maintain the discharge state of an ink jet in good conditions in order to obtain high quality images. That is, since ink constituents are adhered to the head as the head is used, it is necessary to remove the adhered constituents. Conventionally, since head cleaning is carried out when an appointed duration of time elapses or when the image quality is lowered, there are many cases where plates are made with the head becoming dirty. Also, there are many cases where, since the ink constituents are fixed and hardened as regards some ink constituents, it is difficult to remove the ink constituents by normal cleaning unit. In these cases, head stains cannot be removed, wherein cleaning should be frequently carried out, and stains that cannot be removed are deposited, thereby causing the head to quickly become worn.
Further, a system for plotting images in a press is available as unit for making a printing process efficient. Although a method using the above-described laser is available, the method becomes expensive, for which an apparatus is large-sized. Therefore, an attempt has been made to apply a system in which an ink jet system being an inexpensive and compact image plotting unit is employed.
Japanese Patent Application Publication No. 4-97848 discloses a method, in which a plate drum whose surface portion is hydrophilic and lipophilic is employed instead of a prior art plate cylinder, lipophilic and hydrophilic images are formed thereon by an ink jet method and the images are eliminated and cleaned after the printing is completed. However, with this method, removal (easiness of cleaning) of printing images is not compatible with a print resistance property. Also, if an attempt is made to form printing images having a high print resistance property on a plate cylinder, it is necessary to use ink containing resin of comparatively high concentration. Therefore, in ink jetting unit for forming printing images, resin is likely to be fixed at and adhered to a nozzle portion due to evaporation of a solvent, wherein stability of ink discharge is lowered. As a result, it becomes difficult for satisfactory images to be brought about.